Hydraulic transmission systems are widely used in particular in environments where large forces and torques have to be handled. For example, one particular field of application of hydraulic transmission systems is self propelled or mobile working machines, such as construction machines or load lifting machines. Typically, in one such hydraulic transmission system, two or more motors may be connected in parallel to one hydraulic working fluid supply. Further, in case a variable displacement pump is employed as the hydraulic working fluid supply, a high motor torque can be achieved from a relatively small displacement pump, which is important in mobile working machines where space is limited.
In hydraulically operated working systems the flow of hydraulic working fluid supplied to the motors may be controlled either by a hydraulic or by an electronic control or by combinations thereof. This offers flexibility in designing the system according to the specific needs. For example, in a hydraulic system with parallel connected motors in which the flow of hydraulic working fluid in the individual branches is governed by the load on the motors, problems may arise in case one of the motors is not sufficiently loaded and the flow resistance of this transmission branch gets so low that nearly all the hydraulic working fluid supplied by the displacement pump flows through this branch. This may cause “slippage” of the respective motor and the other motor(s) will not receive enough hydraulic working fluid. Attempts to avoid such a situation include the regulation of flow in the individual branches that is controlled hydraulically and/or electronically. One prior art approach is to use flow dividers that split the flow supplied from a pump in predetermined portions at any time. This, however, causes extra pressure drop or resistance in the hydraulic transmission system and increases the overall costs. Further, in most systems, variable displacement pumps are used and also the available flow of the working fluid supply may be controlled according to the specific need and instant load of the system hydraulically and/or electronically so as to achieve optimum performance of the whole system. Yet, often the results leave room for improvements in particular concerning the reduction of complexity while achieving, at the same time, accurate smooth control of the hydraulic system and its components.